There is no set number of pre-trial conferences in a criminal case. The setting of those kinds of hearings can vary from county to county and court to court. A case can be continued by either side for a variety of reasons, and even by the court due to congestion. The best person to ask question is her attorney, if he will agree to answer this. He would be the most familiar with what is going on that might be slowing the case down. If not, then the court clerk can tell you at least the formal reasons, if any, stated for any continuances.
Typically there are one or two pretrial conferences before a matter is set for trial (bench trial before a judge or jury trial before a jury). As much as the accused may want to have this over and be able to leave the state ("skip the state"), the prosecuting and defense attorney seem to be in agreement to continue and if not the court is overruling any objections to continue and siding with the party needing additional time. As long the accused is free and not in custody and defense witnesses and evidence are preserved, the passage of time not caused by the defendant is a criminal defendant's ally. If the defendant wants to exercise their right to a speedy trial they can do so, but at the peril of making their lawyer go to trial unprepared or less prepared than otherwise. If convicted your sister-in-law is facing 0-365 days in jail and/or a $5,000.00 fine. She'll also be prohibited from leaving the state without court or probation's permission even if she gets no jail time and only probation which is often part of any violent crime where someone was battered by a person in a rude, insolent or angry manner.